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Single-pulse transcranial magnetic stimulations (TMSs) of the motor cortex (M1) were performed in order to decipher the neural mechanisms of time preparation. We varied the degree to which it was possible to prepare for the response signal in a choice reaction time (RT) task by employing either a short (500 ms) or a long (2500 ms) foreperiod in separate blocks of trials. Transcranial magnetic stimulations were delivered during these foreperiods in order to study modulations in both the size of the motor evoked potential (MEP) and the duration of the silent period (SP) in tonically activated response agonists. Motor evoked potential area and silent period duration were assumed to reflect, respectively, the excitability of the cortico-spinal pathway and the recruitment of inhibitory cortical interneurons. Shorter reaction times were observed with the shorter foreperiod, indicating that a better level of preparation was attained for the short foreperiod. Silent period duration decreased as time elapsed during the foreperiod and this decrement was more pronounced for the short foreperiod. This result suggests that time preparation is accompanied by a removal of intracortical inhibition, resulting in an activation. Motor evoked potential area decreased over the course of the short foreperiod, but not over the long foreperiod, revealing that time preparation involves the inhibition of the cortico-spinal pathway. We propose that cortico-spinal inhibition secures the development of cortical activation, preventing erroneous premature responding.

The present study was aimed at characterizing the cognitive deficits caused by the degeneration of nigrostriatal dopamine (DA) pathways by using the additive factor logic [Sternberg, S. (1969) Acta Psychol., 30, 276-315], a powerful reaction time (RT) method developed in humans and recently introduced in the rat [Courtiere, A., Hardouin, J., Hasbroucq, T., Possamai, C.-A. & Vidal, F. (2000) Behav. Process., 50, 113-121]. Long-Evans rats were trained to respond to left or right (lateral) visual cues in a choice RT task. Two task factors, signal intensity and force requirement, were manipulated. Partial bilateral 6-OHDA lesions of DA nerve terminals in the striatum were then performed and their effects tested for up to 7 weeks following surgery. Reaction time was lengthened from the 2nd to the 4th week postlesion. This alteration was independent of force requirement, thereby suggesting that the related motor processes were not influenced by the DA depletion. During the 2nd week postlesion, the RT increase was accompanied by a disappearance of the effect of signal intensity, showing that the lesion altered stimulus-related processes. From the 3rd week the signal intensity effect was re-established although RT was still increased, indicating that the stimulus-related processes had recovered while other central processes were still impaired. From the 5th week after surgery, the lesioned animals had completely recovered from the RT deficits induced by the lesion. These results point at the involvement of striatal DA in sensory and central information processes.

Given the large contribution of human error in the failure of complex systems, understanding the source of errors is an important issue. It has been proposed that, in speeded situations, responses biases induce subjects to guess which response will be required. When the guess turns out to be wrong, a fast guess error occurs. In unbiased conditions the possible contribution of fast guess errors remains an open question. We used a response-locked event-related potential ( N-40), assumed to reveal the presence of a response selection process during the reaction time, to probe the presence of a response selection in biased and unbiased situations. The N-40 was present without response bias but absent in biased situations. This lends physiological support to the idea that, in a priming paradigm as used here, most errors in biased conditions are fast guesses whereas most errors result from inappropriate response selections in unbiased conditions. This reveals different sources of errors. [ABSTRACT FROM AUTHOR]

We investigated the influence of temporal preparation on information processing. Single-pulse transcranial magnetic stimulation ( TMS) of the primary motor cortex was delivered during a between-hand choice task. The time interval between the warning and the imperative stimulus varied across blocks of trials was either optimal (500 ms) or nonoptimal (2500 ms) for participants' performance. Silent period duration was shorter prior to the first evidence of response selection for the optimal condition. Amplitude of the motor evoked potential specific to the responding hand increased earlier for the optimal condition. These results revealed an early release of cortical inhibition and a faster integration of the response selection-related inputs to the corticospinal pathway when temporal preparation is better. Temporal preparation may induce cortical activation prior to response selection that speeds up the implementation of the selected response. [ABSTRACT FROM AUTHOR]

In his seminal paper, Donders proposed that Choice reaction time (RT) tasks differ from Go/No-go RT tasks only by the insertion of a response decision operation. We evaluated this possibility by comparing the time course of Laplacian-transformed ERPs, recorded over the primary (M1s) and supplementary motor areas (SMAs) in a Choice and in a Go/No-go task. Laplacian-transformed ERPs showed that a component that develops over the SMAs during the RT of Choice tasks vanishes in our Go/No-go task. This indicates that a process, absent in the Go/No-go task, was 'inserted' in the Choice task. The Choice versus Go/No-go manipulation also modified the motor command: the activity recorded over M1s and the delay separating EMG onset from response completion depended on the nature of the task. This indicates that, although a process was inserted in the Choice task, it was not 'purely' inserted, contrary to Donders' initial assumption. [ABSTRACT FROM AUTHOR]

The event-related potential called 'Error Negativity' (Ne, ERN), which appears when subjects commit errors in choice reaction time tasks, is a marker of response monitoring. By introducing a response probability bias, we show that the Ne is sensitive to response expectancy. We further show that the small negativity evoked by correct responses (Ne-like, CRN) is also sensitive to response expectancy: On unexpected responses, the former decreases while the latter increases to such an extent that the amplitudes of the two components are in the same range of magnitude. Although the sensitivity of the Ne to response expectancy is compatible with the current models accounting for the Ne, the common sensitivity of the Ne and the Ne-like supports the idea that they reflect functionally similar monitoring processes. [ABSTRACT FROM AUTHOR]

In a common version of the Simon task, the subjects respond by a left- or a right-hand key press to the color of a stimulus (S) presented to the left or right of a fixation point. Albeit S location is irrelevant, the incorrect response is more often activated when the required response is contralateral to the S (incongruent) than when it is ipsilateral to the S (congruent). The aim of the present study was to decipher the respective contributions of S-response key location correspondence and S-hand correspondence to such incorrect activations (IAs). The subjects were required to perform a Simon task with the arms not crossing and crossing the median plane. Present for both arm placements, the difference in the frequency of IAs between incongruent and congruent responses was smaller when the arms were crossed. IAs are (i) essentially due to S-key location correspondence and (ii) less influenced by S-hand correspondence. Latency analyses further suggest that intra-hemispheric processing mediates the influence of S-hand correspondence. [ABSTRACT FROM AUTHOR]

In between-hand choice reaction time tasks, the motor cortex involved in the required response is activated while the motor cortex involved in the non-required response is inhibited. Such an inhibition could be implemented actively between the responses defined as possible alternatives by the task instructions or, alternatively, could passively result from some kind of “reciprocal inhibition” between the two motor cortices. The present study addressed this issue. To this end, we compared the surface Laplacian transforms of electroencephalographic (EEG) waves recorded over the contralateral and ipsilateral motor cortices in between-hand and within-hand choice conditions. The dynamics of the recorded EEG activities suggest that inhibition is implemented in a feed-forward manner between the cortical zones controlling the different response alternatives rather than between homologous motor cortical structures. [ABSTRACT FROM AUTHOR]

In a choice reaction time (RT) task, electromyographic (EMG) recordings allowed us to fractionate RT into two subcomponents, namely premotor time and motor time. This has been done for correct trials and errors. The analysis of the EMG burst and motor time (between EMG onset and overt response) showed that the EMG burst amplitude was reduced and the motor time was longer for errors than for correct responses. In the same way as posterror slowing on the RT was interpreted as revealing between-trials changes in executive control, the present data provide direct evidence for an on-line, within-trial, executive control. [ABSTRACT FROM AUTHOR]

Abstract From electroencephalographic recordings, we estimated the surface Laplacian over motor areas in a Stroop-like between-hand choice reaction time task in humans. Response-locked averages showed a (negative) “motor potential” over the primary motor areas contralateral to the response. At the same time, a positive wave was observed over the primary motor areas ipsilateral to the response. These data suggest that, when a between-hand choice is required, an inhibition of the primary motor cortex ipsilateral to the nonresponding hand is implemented. This observation is relevant to the interpretation of the lateralized readiness potential (LRP) because the LRP is blind to the respective contribution of the contralateral and ipsilateral motor cortices. In addition, a negative wave beginning about 200 ms before EMG onset and peaking about 50 ms before it occurred over the supplementary motor areas (FCz). This wave preceded the motor potential, which supports the view that the supplementary motor areas are upstream in a hierarchy of the motor command. [ABSTRACT FROM AUTHOR]

The present study was aimed at deciphering whether the delay in choice reaction time (RT) and the silent period (SP) caused by transcranial magnetic stimulation (TMS) of the motor cortex in the ongoing electromyogram are due to the same physiological mechanism. To this end, the effect of TMS was studied in 6 healthy volunteers performing a between-hand choice RT task. Specific predictions were derived from a logic inspired from the "postponed stages" hypothesis (Pashler & Johnson, 1989). This logic predicts a correlation between SP duration and RT when the stimulated cortex is involved in the response, and a stronger correlation when the stimulation is delivered later during the RT interval. The effect of TMS on RT was twofold: At early stimulation times, the stimulation shortened the RT and this effect was independent of the involvement of the stimulated motor cortex in the subsequent response. At later stimulation times. TMS had a disruptive effect, provided that the stimulated cortex was involved in the response. When the stimulated cortex was involved in the response, there was a correlation between SP and RT; this correlation was stronger when the stimulation occurred later. In contrast, there was no correlation between these two variables when the stimulated cortex was not involved. [ABSTRACT FROM AUTHOR]